The invention is directed to a pulse delay measuring circuit used for measuring the distance to an object.
A pulse delay measuring circuit is discussed in German Publication DE 36 20 226, published July 2, 1987. The circuit disclosed in this German Publication is suitable for laser range finders having a low transmitting pulse energy for the measurement of small, distant, weakly-reflecting, objects.
Under these conditions, the received pulses are very weak and are in some cases smaller than noise signals. An analog-to-digital converter and a parallel adder having a low number of bits is used to improve the signal-to-noise ratio. An advantage of processing a low number of bits is that the processing speed is fast and the circuitry is simple and inexpensive.
If strong pulses are received due to a close or strongly reflecting object, the analog-to-digital converter or, after a few added-together pulses, the parallel adder will be overdriven. This results in the maximum value of the respective output signal being reached within several sampling pulse intervals. As a result, the determination of the peak signal position becomes uncertain.
In a target-locating and range-finding system disclosed in German Patent DE 28 45 164, issued Dec. 15, 1983 to Suzuki, a differentiator is used continuously during digital processing of received pulses.